58 Mr Townsend, The formation of clouds with ozone. 



supposition. The most reasonable explanation of the above ex- 

 periments is that, in the case of the cloud formed with sulphur 

 dioxide, the ozone oxidises the sulphur dioxide, and, with the 

 water vapour present, forms sulphuric acid which causes water to 

 condense and form a drop. A similar explanation holds in the 

 case of iodine where, as is well known, ozone acts on the iodine 

 vapour and acid is formed which plays the same part as the 

 sulphuric acid in the other case. 



A matter of interest in connection with this subject is to 

 enquire whether the centres round which the drops begin to 

 condense are charged. It has been shown (J. S. Townsend, Phil. 

 Mag. Vol. 45, 1898) that the oxygen and hydrogen from a sul- 

 phuric acid electrolyte carry with them an electric charge, and 

 form clouds which have the same properties as those obtained in 

 oxygen which has been deozonised. All these clouds are removed 

 by passing the gases which they contain through a drying agent. 

 The phenomena also resemble one another in regard to the method 

 of increasing the density of the cloud ; thus with the gases from 

 the electrolyte, the density of the cloud is increased by heating 

 the electrolyte in the same way as the cloud obtained by passing 

 ozone through a solution of potassium iodide is increased in 

 density when the temperature of the solution is raised. Experi- 

 ments were made in order to find whether the nuclei are charged 

 in the latter case. For this purpose an aluminium cylinder 30 

 centimetres long and 3 "6 centimetres in diameter was used. The 

 cylinder was provided with an insulated metal rod down its centre, 

 which was connected with a pair of quadrants of an electrometer. 

 The cylinder was raised to a high potential by connecting it to a 

 terminal of a battery of 200 lead cells, the other terminal of which 

 was connected to earth. The quadrants to which the rod was 

 joined were then insulated, having been to earth while the 

 cylinder was being connected to the cells. When the oxygen 

 containing ozone was passed along the cylinder no deflection was 

 obtained on the electrometer scale. A similar result was obtained 

 with oxygen which had been deozonised by potassium iodide 

 solution and dried with sulphuric acid. This gas on escaping 

 from the cylinder formed a cloud in the air of the room, although 

 during its passage through the cylinder no conductivity could be 

 detected by the electrometer. We therefore have no experimental 

 evidence that the centres round which the drops condense are 

 charged. 



In conclusion, I desire to express my thanks to Professor 

 Thomson for many valuable suggestions during the course of these 

 experiments. 



